This invention relates to methods for transmitting and receiving high resolution television pictures, and more particularly to methods for transmitting and receiving high resolution television pictures via signals which are compatible with presently existing moderate resolution television sets and present channel bandwidths. By utilizing the disclosed methods, conventional televisions receive the same quality pictures as they presently do, while modified sets receive pictures at a much higher resolution.
The problem of transmitting/receiving high resolution television pictures is long standing and has many aspects. In particular, one aspect of the problem is that the electromagnetic frequency spectrum must be shared with many non-television uses. Thus, the bandwidth for video signals in domestic television has been limited by government regulation to approximately 4.2 MHz. And the conventional method for transmitting/receiving television pictures limits the resolution of the pictures to the bandwidth of this channel.
Another aspect of the problem of receiving high resolution pictures is that conventionally, an increased resolution requires that the bandwidth of the television's RF and IF and video stages be increased. This, however, is undesirable because an increased bandwidth in the RF and IF stages makes the receiver more susceptible to noise. Accordingly, present television receivers typically do not use the entire 4.2 MHz bandwidth of the electromagnetic frequency spectrum. Instead, most television receivers have a composite RF/IF/video bandwidth of only approximately 3 MHz.
Additionally, there are cost performance tradeoffs which make it impractical to achieve the full 4.2 MHz video bandwidth at a reasonable cost. Technically a full 4.2 MHz video signal could probably be transmitted/received with currently emerging technologies such as SWD's, CCD's and UHF IC's. But the increase in performance which is achieved between displaying signals of 3.0 MHz versus signals of 4.2 MHz is probably too marginal to justify the added expense. What is needed is a method for achieving much more significant improvements in the picture resolution (i.e., -double or triple the resolution).
In the prior art, various methods have been devised for transmitting high resolution television pictures over a narrow band channel. However, the signals which are transmitted in these methods are not compatible with present commercial television receivers. For example, one such method for transmitting high resolution pictures over a narrow channel is known as delta modulation. In delta modulation, the video signals which are transmitted contain information indicating the difference between the light intensity of successive frames. Accordingly, in a still scene, the light intensity from frame to frame is relatively constant, and thus the bandwidth of the video signals is small. However, these video signals are clearly not compatible for use within present television receivers for home use.
It is therefore one object of the invention to provide a method for transmitting/receiving high resolution television pictures via signals which are compatible with presently existing commercial television.
Another object of the invention is to provide a method of transmitting/receiving television pictures having a resolution of at least double the resolution of present commercial television pictures.
Another object of the invention is to provide a method of transmitting/receiving television pictures having frequency components which are greater than the bandwidth of the electromagnetic frequency spectrum over which they are transmitted.
Still another object of the invention is to provide a method of transmitting/receiving high resolution television pictures which is operable in a television receiver having a relatively narrow bandwidth RF/IF stage.